Manufacture of Thermoelectric Generators and Other Devices That Include Metastructures

This application is a divisional of U.S. patent application Ser. No. 18/027,449, filed on Mar. 21, 2023, which is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/EP 2021/076337, filed on Sep. 24, 2021, which claims priority and benefit from U.S. Provisional Patent Application No. 63/085,431, filed on Sep. 30, 2020, the contents and disclosures of which are incorporated herein by reference in their entirety.

The present disclosure relates to the manufacture of thermoelectric generators (TEGs) and other devices that include metastructures.

The thermoelectric effect refers to the energy conversion process between thermal and electrical energy. A potential advantage of thermoelectric power generation is the sustainable and reliable conversion of thermal energy into electricity with no moving parts. Thus, in view of the increasing demand for wireless sensor networks and small consumer electronics powered by what would otherwise be wasted heat, TEGs have received attention as a source of sustainable power supply.

Thermoelectric materials, which can be used to generate power directly from heat by converting temperature differences into electric voltage, preferably should have both high electrical conductivity and low thermal conductivity. Low thermal conductivity ensures that when one side becomes relatively hot, the other side stays relatively cold, which helps to generate a large voltage in the presence of a temperature gradient. The measure of the magnitude of electrons flow in response to a temperature difference across that material can be indicated, for example, by what is known as the Seebeck coefficient(S).

The present disclosure describes techniques for manufacturing TEGs and other devices that include metastructures. Metastructures, which also may be referred to as metasurfaces, refer to surfaces with distributed small structures such as a distributed array of nanostructures. As described in greater detail below, the techniques can include imprinting curable thermo-electrical materials to form the metastructures.

For example, in one aspect, the present disclosure describes a method that includes imprinting a first replication layer to form a first metastructure of first meta-atoms, and imprinting a second replication layer to form a second metastructure of second meta-atoms. The first replication layer is composed of nanoparticles embedded in a polymer, and is disposed on a surface of a first substrate that includes first electrical contacts. The second replication layer also is composed of nanoparticles embedded in a polymer, and is disposed on a surface of a second substrate that includes second electrical contacts. The method further includes bonding meta-atoms of the second metastructure to the first electrical contacts, and bonding meta-atoms of the first metastructure to the second electrical contacts, such that respective ones of the meta-atoms of the first metastructure are connected electrically in series with respective ones of the meta-atoms of the second metastructure.

In another aspect, the present disclosure describe a method that includes imprinting a first replication layer to form a first metastructure comprising first thermoelements, and imprinting a second replication layer to form a second metastructure comprising second thermoelements. The first replication layer is composed of nanoparticles embedded in a polymer, and is disposed on a surface of a first substrate that includes first electrical contacts. The second replication layer also is composed of nanoparticles embedded in a polymer, and is disposed on a surface of a second substrate that includes second electrical contacts. The second replication layer has a conductivity type opposite that of the first replication layer. The method further includes bonding the second thermoelements to the first electrical contacts, and bonding the first thermoelements to the second electrical contacts, such that respective ones of the first thermoelements are connected electrically in series, and thermally in parallel, with respective ones of the second thermoelements.

In some implementations, the first replication layer and the second replication layer have the same composition as one another, whereas in other implementations, the first replication layer and the second replication layer have different compositions from one another.

Some implementations include one or more of the following features. For example, imprinting the first replication layer can include pressing a first stamp into the first replication layer, and imprinting the second replication layer can include pressing a second stamp into the second replication layer. In some implementations, the method includes curing material of the first replication layer after pressing the first stamp into the first replication layer, and curing material of the second replication layer after pressing the second stamp into the second replication layer. Further, some implementations include removing the first stamp after curing the material of the first replication layer, and removing the second stamp after curing the material of the second replication layer.

In some implementations, the method includes, prior to the bonding, aligning the first and second substrates such that the second meta-atoms (e.g., thermoelements) are aligned with exposed portions of the first electrical contacts, and such that the first meta-atoms (e.g., thermoelements) are aligned with exposed portions of the second electrical contacts.

In some implementations, at least one of the polymer of the first replication layer or the polymer of the second replication layer is a curable resist. In some implementations, at least one of the polymer of the first replication layer or the polymer of the second replication layer is a photocurable resist. In some implementations, at least one of the polymer of the first replication layer or the polymer of the second replication layer is a thermally curable resist.

In some implementations, the nanoparticles of at least one of the first replication layer or the second replication layer include bismuth chalcogenides. In some implementations, the nanoparticles of at least one of the first replication layer or the second replication layer include bismuth telluride. Other materials for the replication layers may be used in some instances.

In some implementations, the method further includes applying a heat treatment to at least one of the first or second meta-atoms (e.g., thermoelements) to increase a density of the nanoparticles. Applying the heat treatment can include, for example, sintering.

In some implementations, after the bonding, the first and second substrates, the first and second electrical contacts, and the first and second thermoelements, form parts of a thermoelectric generator module. The method can include, for example, incorporating the thermoelectric generator module into a health-related sensor device or incorporating the thermoelectric generator module into a wearable device.

Some implementations include one or more of the following advantages. For example, the use of imprinting can, in some implementations, facilitate relatively inexpensive mass production of TEG or other modules. Further, the technique can, in some cases, avoid the need for etching steps, thereby resulting in a simpler manufacturing process. Further, in some instances, efficiency of the TEG modules may be enhanced.

Other aspects, features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims.

1 FIG. 10 10 12 14 12 14 12 14 12 14 illustrates a schematic of a TEG moduleincluding a circuit containing thermoelectric materials that generate electricity from heat directly. The TEG moduleincludes two dissimilar thermoelectric materials,joined at their ends and configured as a thermoelectric generator: an n-type semiconductor (with negative charge carriers)and a p-type semiconductor (with positive charge carriers). Thus, the materials,have different Seebeck coefficients from one another. Direct electric current flows in the circuit when there is a temperature difference between the ends of the materials,. In general, the current magnitude is directly proportional to the temperature difference.

2 FIG. 10 16 16 16 18 20 10 22 As shown in, the TEG moduleincludes multiple pairs of n-and p-type thermoelementsthat form legs so as to facilitate generation of sufficient electrical power to operate, for example, small consumer electronic devices (e.g., wearable devices). The n-and p-type thermoelementsare connected electrically in series, and thermally in parallel, with one another. The thermoelementsalso are connected to electrically conductive (e.g., metal) interconnects, which can be disposed on substrates. The modulefurther can include electrical wiresto provide the electrical output.

16 As described below, a technique for manufacturing solid state TEG modules includes imprinting a curable thermo-electrical material to form the legs (i.e., the thermoelements) of the TEG generator. “Imprinting,” as used in this disclosure, may include, for example, one or more of embossing, debossing, stamping, or nano-imprinting. The use of imprinting can, in some implementations, facilitate relatively inexpensive mass production of the TEG modules. Further, the technique can, in some cases, avoid the need for etching steps, thereby resulting in a simpler manufacturing process than at least some other processes. Further, in some instances, efficiency of the TEG modules may be enhanced.

3 3 FIGS.A andB 30 30 32 32 32 32 30 30 As shown in, electrical contactsA,B, respectively, are deposited and patterned in or on first and second substratesA,B. The substratesA,B can be composed, for example, of a relatively flexible material (e.g., a cured resist) or a relatively rigid material (e.g., silicon or fused silica). The electrical contactsA,B preferably are composed of a metal or other material that exhibits relatively low contact resistance (e.g., gold or silver).

4 4 FIGS.A andB 34 34 32 32 30 30 34 32 34 34 32 Next, as shown in, a respective replication layerA,B containing a mixture of nanoparticles and a polymer is deposited over each of the substratesA,B, in particular over the surface on which the electrical contactsA,B respectively are present. Examples of methods for depositing the replication material include printing (e.g., inkjet printing), jetting, dispensing, screen printing, dip coating, and spin coating. The replication layerA, which contains an n-type mixture of the nanoparticles and polymer, is deposited on a surface of the first substrateA, whereas the replication layerB, which contains a p-type mixtureB of the nanoparticles and polymer, is deposited on a surface of the second substrateB.

34 34 2 3 3 The nanoparticles in the replication layersA,B preferably are composed of a high efficiency thermoelectric semiconductor material such as bismuth telluride ((BiTe). In some implementations, other materials can be used for the nanoparticles. For example, in some cases, the nanoparticles are composed of other bismuth chalcogenides,, lead tellurides, inorganic clathrates, skutterudites (e.g., CoSb), half-Heusler alloys, compounds of Mg and group-14 elements, oxide thermoelectric semiconductors, or other thermoelectric semiconductors. In some instances, the composition of the nanoparticles includes nanocomposites containing nano-inclusions, and any of the aforementioned materials as the matrix.

34 34 The polymer in the replication layersA,B can be, for example, a curable resin. In some implementations, the polymer is a photoresist or thermal resist that is curable (e.g., photo-curable and/or thermally curable). In some implementations, other materials can be used for the polymer.

5 5 FIGS.A andB 6 FIG.A 6 FIG.B 34 34 36 36 34 34 36 34 38 36 34 38 34 34 As shown in, following deposition of the replication layersA,B, imprinting tools (e.g., stamps)A,B are pressed, respectively, into a respective one of the layersA,B to form the n-type and p-type thermoelements. In particular, the first imprinting stampA is pressed into the layerA and cured to form n-type meta-atoms (i.e., thermoelements)A (see), and the second imprinting stampB is pressed into the layerB and cured to form p-type meta-atoms (i.e., thermoelements)B (see). Thus, the imprinting process can include pressing a structured surface of a stamp into a replication material in which nanoparticles are embedded, curing the replication material, and removing the surface of the stamp from contact with the replication material. The curing process may include, for example, a photo-cure and/or a thermal cure, depending on the type of polymer used in for the replication layersA,B.

36 36 36 36 36 36 36 36 The stampsA,B may be composed of a variety of materials such as a cured replication material and/or a patterned semiconductor wafer (e.g., a patterned silicon wafer), which in some cases can include deposited metal layers. In some implementations, one or both of the stampsA,B are transparent (e.g., are composed of glass). In some implementations, one or both of the stampsA,B are thin and/or flexible (e.g., composed of polycarbonate foil). In some implementations, the structured surface of one or both of the stampsA,B is composed of a polymer (e.g., polydimethylsiloxane (PDMS)).

36 36 30 30 36 36 30 30 32 32 36 36 30 30 Each of the stampsA,B can have a respective pattern or other arrangement of features that represents an inverse image of the pattern or other arrangement to be imprinted into the respective replication layerA,B. When the stampA,B is brought into contact with the replication layerA,B and is pressed towards the substrateA,B, the imprinting imparts an inverse image of the features on the surface of the stampA,B into the replication layerA,B.

34 34 In some instances, after removing the stamp from the replication layersA,B, the nanoparticles can be sintered, or some other heat treatment can be applied, so as to increase the density of the meta-atoms. In some cases, sintering the meta-atoms may result in the coalescence of the nanoparticles and removal of at least a portion of the polymer contained in the replication material. In some instances, the sintering or other heat treatment can be performed at a later stage in the process.

38 38 30 38 38 30 39 38 39 38 38 38 6 FIG.A 6 FIG.B 6 FIG.A 6 FIG.B The resulting n-type meta-atomsA, which serve as n-type thermoelements, form a first metastructure, with each of the thermoelementsA on a respective one of the electrical contactsA (see). Likewise, the resulting p-type meta-atomsB, which serve as p-type thermoelements, form a second metastructure, with each of the thermoelementsB on a respective one of the electrical contactsB (see). Thus, one sub-assemblyA () includes a metastructure composed of n-type thermoelementsA, and a second sub-assemblyB () includes a metastructure composed of p-type thermoelementsB. The size of the thermoelementsA,B may depend on the material, but typically is in the range of 10 nm-300 nm, and preferably should be in the range of 10-100 nm. The size of the metastructure preferably is such that the thermal conductivity is substantially reduced, whereas the electrical conductivity is substantially unaffected or at least is not impacted adversely.

7 FIG.A 39 39 38 39 40 30 39 38 39 40 30 39 As shown in, one of the subassemblies (e.g., subassemblyB) is flipped over and is aligned over the other one of the subassemblies (e.g., subassemblyA). In the illustrated example, the thermoelementsB of the second subassemblyB are aligned above exposed portionsA of the electrical contactsA in the first subassemblyA. Likewise, the thermoelementsA of the first subassemblyA are aligned below exposed portionsB of the electrical contactsB in the second subassemblyB.

39 39 30 30 38 38 38 30 38 30 38 38 30 30 18 22 39 39 30 30 38 38 30 30 38 38 7 FIG.B 2 FIG. 2 FIG. Next, the two subassembliesA,B are brought into contact with one another, as shown in. The subassemblies can be heat-treated so as to bond the electrical contactsA,B and thermoelementsA,B to one another. In particular, the thermoelementsB are bonded to the electrical contactsA, and the thermoelementsA are bonded to the electrical contactsB. Thus, in the resulting assembly, the n-and p-type thermoelementsA,B are connected electrically in series, and thermally in parallel, with one another, such that the electrical contactsA,B serve as the electrical interconnects (i.e., the interconnectsin). Electrical wires (e.g., wiresin) can be provided to the assembly for the electrical output. In some instances, the heat treatment applied to the subassembliesA,B to bond the electrical contactsA,B and thermoelementsA,B to one another also can result in an increase in the density of the meta-atom (e.g., by causing the nanoparticles to coalesce). In some cases, the heat treatment applied to the subassemblies sinters the meta-atoms and causes the nanoparticles to coalesce. In some implementations, two different heat treatments may be performed sequentially at this stage in the process. That is, a first heat treatment can be performed to bond the electrical contactsA,B and thermoelementsA,B to one another, and a second heat treatment can be performed to sinter the meta-atoms and/or cause the nanoparticles to coalesce. In some cases, the order of the heat treatments may be reversed.

TEG modules, such as those described above, can be used for heat harvesting in a wide variety of devices and applications, including wearable devices in which the user's body heat is harvested and used by the device. For example, some sensors are capable of monitoring a patient's health conditions. An important requirement for many of these medical sensors is a stable and continuous power supply. Thermoelectric devices capable of generating power by harvesting heat from a human body can be used for that purpose. In particular, the TEG modules described in this disclosure can be integrated with medical and other health-related sensor devices, as well as a wide range of other small consumer electronic devices.

Further, substantially the same configuration described above can be used as a heating and/or cooling device. In such implementations, instead of applying a thermal gradient, a voltage is applied. Such a module may be used, for example, as a micro cooling element for medical applications or integrated into (or placed adjacent) electronic circuitry.

3 8 FIG.A through 30 30 38 38 Although the foregoing process described in connection withcan be particularly advantageous for manufacturing TEG modules that include thermoelectric elements of different conductivity types, a similar process can be employed to manufacture devices that include respective metastructures connected together electrically in series. For example, the same technique as described above can be used even where the material of the replication layerA is the same as the material of the replication layerB. Thus, the foregoing technique can be used to fabricate modules that include multiple metastructures composed of the same, or different, material(s). As described above, the meta-atomsA,B of the metastructures are bonded to electrical contacts such that the meta-atoms of the metastructures are connected electrically in series.

Various modifications will be readily apparent and within the spirit and scope of this disclosure. Accordingly, other implementations are within the scope of the claims.

What is claimed is: